1. Technical Field
The present invention relates to methods for metering the flow of fluid from a source to a load, and to apparatus adapted for use therewith. More particularly, the invention pertains to such subject matter employing an electrohydraulic solenoid secured to and in fluid communication with a metering valve body which defines a fluid channel in which a metering valve is positioned to directly and partially block a flow path between the source and the load.
2. Related Art
The use of solenoids and solenoid/valve combinations in metering the flow of fluid between a source and a load is known, as is illustrated by U.S. Pat. Nos. 4,386,553 Thoman et al. and 4,640,093 Eastman.
U.S. Pat. No. 4,640,093 discloses a system that directly meters fuel to a turbine engine by opening a control port in response to pulses applied to a solenoid to provide an average flow area that is proportional to the duty cycle of the pulses. The range of flow rates over which the system may be precisely operated is suspect because of the use of a secondary flow path which is employed at or above a certain required flow rate. The relatively sudden use of this flow path may produce sudden spikes in metered fuel flow and complicate the calibration process. Moreover, the use of diaphragms in the system may render it less robust and more limited in its range of application as compared to the present invention.
U.S. Pat. No. 4,386,553 discloses a control system for a doser actuator in which a pair of solenoids is used to variably pressurize two chambers in fluid communication with a reciprocating piston-pair member. The fluid pressures in the chambers apply opposing hydraulic forces to the piston-pair member in order to vary its position in a stepped channel. The system effects metering by using the piston-pair member as an actuator that controls the position of a fuel metering valve by unspecified means. The system requires more solenoids and consequently more cumbersome control circuitry than the present invention which, as will be evident from the following description, provides a more functionally-integrated approach to metering fluid flow.